Method and system for television communication



Jan. 26, 1943.

J. H. HOMRIGHOUS METHOD AND SYSTEM FOR TELEVISION COMMUNICATION 2 sheets-sheet 1 Filed Nov. 28 1939 /3 5 7 MO 0. POWE R 6 AMP. AMP

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Jan. 26, 194?. .1. H. HOMRIGHOUS 2,309,393

METHOD AND SYSTEM FOR TELEVISION COMMUNICATION Filed NOV. 28, 1939 2 Sheets-Slieet 2 cred fun. it

MlE'llHUD A SYSTEM FOR TELEWSKUN m i i i CA'JNUN 6 Claims.

My invention relates to methods for narrowing the frequency band used in television; also relates to methods of synchronizing the scang devices used in television.

Accordingly, one of the main objects is the provision of a method for transmitting and reproducing control or synchronizing signals as video or picture signals.

Another of its main objects is for televising certain characters or signs in the television picture that can be used for keeping television receivlng sets in synchronization with the television transmitter.

Another object of my invention is the provision of means for definitely relating the sweep frequencies to the field or frame frequencies and not necessarily to that of time.

Another object of my invention is the provision of means for altering the number of pictures in a given time to eliminate interference.

Another object of my invention is the generation of the sweeps at both the transmitting and receiving stations whereby the sweeps at the receiver are under the control of certain characterns or designs televised as video or picture Signa Another object of my invention is to narrow the frequency band required for television by combining the picture with the control or synchronizing characters in one set of video signals.

Another object of my invention is to use a very narrow frequency band when televising only characters or signals.

Another object of my invention resides in an improved method and system for television communication, by which the video or picture symbols can be transmitted by wireless over ,substantially greater distances than is possible with the present methods and systems.

Several methods for transmitting control frequencies have been used or devised; for instance. control frequencies have been transmitted separately from the picture or video frequency either as a separate modulation of a separate carrier frequency, or in the interval between successive pictures or lines of the pictures. Another method has been to have a band in the picture so that the picture currents are in distinct groups which are used for synchronizing. A further method is in use whereby full black of the picture will be approximately 80% of the maximum amplitude. Still a further method has been devised whereby the scanning operation produces the control frequencies as a modulation of the video currents and a filter at the receiver removes the effect of such frequency from the picture. These methods are all very complicated and cause considerable dimculties.

According to my present invention, picture s nals are combined with control signals in such a manner that both are transmitted and reproduced as picture or video signals, thereby greatly simplifying the equipment and circuits used, and also insuring absolute synchronization of the scanning operations. This is accomplished by generating the sweeps and blanking frequencies at both the transmitter and the receiver, and having the voltage waves at the respective line and field frequencies and blanking frequencies generated at the receiver. and controlled by televising certain characters and translating these into proper frequencies at the receiver, and also by having the equipment for producing the characters at the transmitter definitely locked in step with its generating equipment. These frequenciesare applied to produce the scanning action of the pick up tube at the transmitter and the scanning action of the viewing tube, so that the electron ray in the transmitting and receiving tubes will always be in synchronism durin the scanning operation. Because of this positive method or system of synchronizing both line and frame frequencies a much higher interlace ratio is possible. which may result in reducin the number of fields from the present practice of 60 to 48 per second and still maintain a high definition picture. This would materially reduce the frequency band required. The height of the picture would be increased as it would not be necessary to reserve any space for ynchronizing pulses. i

Still another advantage of this system is that a definite number of lines per frame or field is predetermined, but the number of frames or picture changes may be altered to eliminate interference or change the frequency band.

This invention will be better understood by referring to the following description taken in connection with the accompanying drawings in which:

Figures 1 and 2 are simplified diagrammatic views of a television transmitting station and a television receiving station respectively, illustrating the principles of this invention.

Figure 3 is a motor device for generating control frequencies and for producing certain characters for televislng.

Figure 4 is an end view of one of the character forming members shown in Figure 8.

Figure 5 is an end view of disk shown in Fisure 3 for generating line and other control frequencies.

Figure 6 shows the characters for televisin to synchronize the scanning operations at the receiver with those at the transmitter.

Figures 7 and 8 show circuits for use in my invention.

Figure 9 shows a motor driven device for generating control frequencies at the receiver with circuits for controlling the motor from reproduced characters.

Figure 10 shows the control characters reproduced at the receiver.

Figure 11 shows another arrangement at the cathode ray receiving tube.

In Figure 1 the numeral 1 designates a cathode ray transmitting tube of conventional type, and is known as an iconoscope, or it may be a tube known as an image dissector, and as illustrated it comprises a mosaic, photo-electric screen on which a light image of the object is projected and an electron gun for generating a ray of electrons directed at the screen, and two sets of deflecting plates for deflecting the electron ray at the line and field frequencies, so that it is caused to scan the screen. The picture and certain other characters are thereby developed and fed by an output connector 2 to a modulating amplifier 3.

A carrier wave is provided by an oscillator it. In the power amplifier 5 this carrier wave is modulated by the frequency band video or picture signals through the modulation amplifier 3. The signals from the amplifier 5 are supplied by a connection 6 to the antenna I.

The control signals are transmitted as video signals which will appreciably reduce the frequency band now required for television.

At the receiving station shown in Figure 2, the antenna 8 receives the carrier signals from the transmitter antenna 1 to a radio frequency amplifier 9. An oscillator i reacts with these signals in the first detector stage H on the superheterodyne principle to produce an intermediatefrequency which is supplied to the video intermediate-frequency stage l2.

After suitable amplification, the video signal is detected at l3 and applied by a connection It to a scanning device l5. The device I5 is represented as being in the form of a cathode-ray tube of a common construction, and comprises a fluorescent screen IS, an electron gun for developing a ray of electrons directed at the screen, and two sets of electrostatic plates for deflecting the electron ray at the line and field frequencies to cause it to scan the screen. The video signals are applied to a control electrode of the electron gun, whereby, the intensity of the electron ray is made to vary with, the video or picture signals.

The fluorescent screen I6 is scanned by yarious devices in order to translate the characters therea on into control signals to be more fully explained hereinafter.

Referring to Figure 3, the numeral l1 represents a motor, which is operated from the house current, and runs at approximately 900 R. P. M. I8 is a drum having two black bands I9 and 23 each of which extends over one-half of the periphery of the drum i8, or through an angular distance of two fields as shown in Figure 4. The two bands are located adjacent the opposite edges of the drum, respectively, so that by rotating the drum in front of the transmitting tube two black vertical lines will appear alternately, but separated on the mosaic, as shown in Figure 6 by the numerals 2| and 22. Thus drum IB may be known as a code sender. Thus it will be seen that each mark or sign on the mosaic will be definitely identified with a frame or picture change, and also definitely related to the speed of the motor or 30 picture change for 900 R. P. M. of the motor. These marks will be reproduced in the receiver, where they will be used to generate current, for control purposes to be further explained later.

The representation of the images shown in Figure 6, and other figures having similar representation, applying to the transmitting tubes, are shown similar to the way that they are reproduced for clearness. It is to be understood that the lens system of the transmitting tube will change the image location.

The short horizontal line 23, Fig. 6, shown above the vertical control characters, is a permanent mark either on the mosaic of the transmitting tube M, Figure 1, or outside the lens system of the tube at 25. The purpose of this short horizontal line, which is repeated in all the pictures, is for automatically keeping the receivers in proper phase relation which will be more fully explained later.

The disk 26 is mounted on the motor shaft and has four holes of equal arcs apart near its periphery which are rotated past a source of light 21, directed toward the photo-electric cell 23, which generates pulses of current for field scanning that are definitely tied in with the speed of the motor. That is, each revolution of the motor will produce four fields as well as four pulses, and by the adjustment of the photo-electric cell, these pulses are generated just at the exact instant required. Likewise the disk 29 is rotated by the motor i1 between the sources of light 30 and 32 and the photo-electric cells 3| and 33, respectively, to generate line scanning and blanking frequencies.

In Figure 5, I have shown an end view of disk 29, divided into four equal divisions which represent four fields, or two picture changes, which is easily arranged for any number of lines per field by the number of holes in each field division of disk; also by altering the position of the holes consecutive or progressive line scanning may be obtained as well as interlace of 1 to 2 ratio or 1 to 4 ratio which would also require reducing or adding to the number of openings in disk 26 for vertical scanning. The line blanking frequencies are obtained from the photo cell 33, controlled by the same openings as cell 3|, but positioned in another location at the disk, so that both cells will be operated from similar field openings; likewise vertical blanking may be obtained from another photo cell operated from the disk 26. As shown in Figure 5, field A has 220 openings and field B has 221 openings, so positioned that the openings in field B are advanced ,a distance equal to one half of the space between the holes.

From the above description, it will be seen that the pulse for line scanning is definitely locked with the speed of the motor. Therefore any change in speed of the motor does not alter the number of openings per field or per frame. and by slightly changing the speed from sixty cycle operations it is possible to avoid interference from the local sixty cycle power supply and its harmonics.

A system or circuit for producing the proper sweep signals is shown in Figures 7 and 8. In Figure 7, I have shown a photo cell M, which may be either cell 28 or 3| in Figure 3. This cel it is responsive to the variation of light energy caused by the rotation of the disk it or 29 to cause grid excitation of amplifier tube 35. The anode of tube 35 is connected, through a winding of transformer 36, to the positive terminal of the voltage divider 31. The voltages induced in the secondary windings of frequency or pulse of current from the transformer 36 drive the grid of tube 38 positive, discharging the condenser 39] through the tube. Thus by alternately charging the condenser 33 through resistance M and discharging it through the tube a saw tooth wave is generated. The vertical sweep frequency, caused by disk 2%, is fed through conductor ll to the conductor M at the transmitting tube in Figure 1. Ihe line sweep frequencies generated by disk 2% are transmitted through conductors ll and M to the transmitting tube.

In Figure 9 I have shown two disks to and M and associated photo cells and M respectively which are exactly like those shown in Figure 3 and need no further explanation. These disks and tubes together with the circuits of i and t are for generating the sweep signals for the cathode ray receiving tube it, Figure 2. The disks M and M are directly connected to the motor 52. Therefore the frequencies generated are directly related to the speed of the motor.

Referring to Figure 10, I have shown two frames, representing the control signals or marks, similar to those described in Figure 6. We will assume to start, that the receiver is in synchronismwith the transmitter, and that the vertical lines or characters are coming through in perfect order. Therefore line 53 will be as shown in frame 5d and line bill will be as shown in frame 5%. These lines will continue to alternate every picture change during the television program or broadcast. Now as the picture is scanned from top to bottom and due to the direction of rotation of the wheel at the transmitter the line or mark will disappear later at the lower end than at any other portion of the character. Therefore rays of light are directed'from these lower mark extremities on the fluorescence screen it, by the aid of a mirror 5i and suitable lenses to photo electric cells 58 and 59. Since these markswill alternate 0n the receiving tube screen in the exact likeness as they are transmitted, an alternating current may be generated in synchronism with the picture changes.

With further reference to Figure 9, I have shown circuits for producing an alternating current from the variations of light intensities occurring in the photo cells 58 and 59 which may be the same ones shown in Figure 10. These photo-cells control the grid excitation of grids Eli and M of amplifier tubes 62 and t3; the anodes 6d are connected in parallel through the primary winding of transformer 65, to the positive side.

of the voltage divider 6G. The cathodes 61 are connected in parallel to an intermediate point of the voltage divider 66. The cathode 65 of photo cell 58 is connected to the grid 60 of amplifier t2 and through resistance $9 to negative potential at the voltage divider, thereby maintaining the grid 60 at a negative potential with respect plaining this more in detail, the mark or characto cathode 61 and plate 6%. The circuit is so arranged, therefore, that an increase in the intensity of light on the photo-cell 58 will increase the plate current of tube 62. The photocell 59 has its anode 10, connected to the grid iii of amplifier tube 63, and is maintained at a positive potential with respect to its cathode N. This causes a decrease in the plate current of and suitable lenses tube t3, upon increasing the intensity of light directed toward the photo-cell 59. Other amplifler tubes may be connected in parallel to increase the amplification. Therefore it will be seen that the marks 53 and 55 shown in Figure 10 will alternately operate the photocells. Ex-

ter 53 in frame 56 does not reflect enough light into photo cell 58 to produce any effect, but the light reflected from the location of the alternate mark 55 into photo-cell 59 causes a decrease in the current value in tube 53. Next considering the frame 56, following frame it, the line or mark 55 occurring in the opposite location does not reflect suficient light to the cell 59 to produce any effect. However, tube 58 will receive light from the blank space previously occupied by line 53, therefore producing an increased current at tube 62. The plate circuits of tubes 62 and 63 are connected in parallel and hence a continuously rising and falling current is produced in the primary winding of transformer 65, whereby alternating voltages are induced in the secondary winding. These voltages are fed to the inverter circuit consisting of tubes 12 and 13 each of which is provided with an anode M and indirectly heated cathode I15 and a control electrode or grid W. The grids K6 are normally biased negatively by a battery 1'! through the resistance l8 and W. The grid excitation voltage is supplied through transformer 55. Direct current is supplied through conductor 80, choke 8| to mid point of primary winding of transformer 32, thence divided through the two halves of this winding to the anodes "M, a condenser 83 being connected across the primary winding of transformer M. The cathodes 15 are connected to the source of direct current supply through conductor M. The secondary winding of transformer 82 is connected through the contact of the control relay $5 to the motor 52 which causes the motor to run at the speed of the picture changes or in synchronism with the motor at the transmitter, producing the control characters.

With reference to Figure 10, the short horizontal line 85 is produced from the permanent mark it or 25 at the transmitting tube and will occur in all fields, picture changes or frames. The purpose is to give automatic regulation for phase control. The mark 86 is located between two marks 53 and 55 on the screen it of the receiving tube Iii. From a point, just at left of this horizontal line at, when in proper phase relation a ray of light is directed by mirror 81 to a photo cell 88. This photo cell may be used in the circuit of Figure 7 which has previously been described. The transformer 36 now has its secondary winding, 89, connected through control relay 85. Should the motor at the receiver get out of phase and lag behind the motor at the transmitter the line 86 would move to the left causing thephoto cell to remain inoperative and also the relay 85; however, should the motor 52 get out of phase in the opposite direction, the line 86 would move to the right, causing light to enter photo cell 88, which will operate relay 85 to include the resistance 90 momentarily in the motor circuit, thereby correctlng the phase relation.

The operation of the receiver is as follows: the motor 52 is started through the local power supply, which will produce the control frequencies including sweeps as has been described. The operator, through the rheostat 9| will slow the motor down, until the vertical control characters t3 and Eli begin to appear on the right side of the screen I 6, in approximately the proper location vertically, whereupon the local power supply will be shut ofi, and the photoelectric device will now generate electrical oscillations from the periodically changing control characters on the screen to control the frequency of altemating current generated by the amplifiers l2 and 13 through the transformer 82 to the input circuit of motor 52, which will bring the motor into synchronism with the picture changes; the mark 86 will be moved to the extreme top of the picture as soon as the motor starts to operate from the tube supply. The picture, produced from this system will be of greater height than those at present in use, on account of no space being taken between each field for synchronizing pulses as in the present systems. The line 86 may then function to adjust the horizontal scanning at the receiver in proper phase relation.

It will be understood that numerous modifications are possible without departing from the spirit of my invention or the scope of the claims.

Having thus described my invention, I claim:

1. In a television system, a transmitter, means for producing difierent light values and for periodically interchanging these light Values at a point within the view of said transmitter and at a frequency which bears a fixed relation to the scanning frequencies at said transmitter, a receiver for producing an image from received signals in which said interchanging light values are reproduced along with the view, a photoelectric device sensitive to the interchanging light val-' ues, means controlled by said device for generating alternating current, and means including a motor driven from said current for gen-- erating scanning potentials for said receiver.

2. In a television system, a cathode ray camera tube having an image plate and an electron ray directed toward the image plate, a motor, means for moving the said electron ray to scan the said image plate including mechanism driven by said motor, said mechanism provided with apparatus and suitable circuits to control the movement of the said electron ray in a vertical direction and in a horizontal direction, and means driven by said motor having two characters alternately appearing in the view of said camera tube to produce images of the two characters alternately on the said image plate bearing a,

fixed relation to the vertical movement of said electron ray.

3. In a television system, a cathode ray camera tube having an image plate and an electron ray directed toward the image plate, a motor, means for moving the said electron ray to scan the said image plate including a pair of disks driven by said motor, one of said disks provided with apparatus and suitable circuits to control the movement of said electron ray in a vertical direction, and another one of said disks divided into field scanning sections provided with apparatus and suitable circuits to control the movement of said electron ray in a horizontal direction to scan odd line location on said image plate in accordance with one of the field sections, and to scan even line locations on said image plate in accordance with another one of the field secaeoasas tions, and a code sender driven by said motor having two black characters alternately appearing in the view of said camera tube to produce images of the two characters alternately on the said image plate bearing a fixed relation to the vertical movement of said electron ray.

4. In a television system, a cathode ray viewing tube provided with a screen, a motor, means including mechanism driven by said motor for scanning said screen in successive periods to produce images from received picture signals, said images including two control characters appearing alternately, a current supply circuit, means for transmitting energy from said supply circuit to said motor, including a plurality of electron tubes provided with control grids, a photo electric device for producing electrial oscillations for exciting said control grids to determine the frequency of alternating current delivered by said means for transmitting energy, said device, sensitive to the variations in light from the al temate appearance of said control characters, to vary the frequency of said electrical oscillations to control the speed of said motor.

5. In a television receiving system for produc ing successive field images from received signals,

said system comprising means to produce a variable electron ray for scanning a receiving screen, a photo electric device sensitive to changes in light values in successive field images on said screen, means controlled by said device for generating alternating current, a motor driven from said current, means for moving said electron ray to scan said screen including a pair of disks rotated by said motor, one of said disks provided with apparatus and suitable circuits to control the movement of said electron ray in a vertical direction, and another one of said disks, divided into field scanning sections, provided with apparatus and suitable circuits to control the movement of said electron ray in a horizontal direction to scan odd line locations on said screen in accordance with one of the field sections, and to scan even line locations on said image plate in accordance with another one of the field sections.

6. In a television system, a cathode ray viewing tube provided with a, screen, a motor, means including mechanism driven by said motor for scanning said screen in successive periods to produce images from received picture signals, said images including a. mark, and two control characters appearing alternately, a current supply circuit, means for transmitting energy from said supply circuit to said motor, including a plurality of electron tubes provided with control grids, a photo electric device for producing electrical oscillations for exciting said control grids to determine the frequency of alternating current delivered by said means for transmitting energy, said device sensitive to the variations in light from the alternate appearance of said control characters, to vary the frequency of said electrical oscillations to control the speed of said motor, and means controlled by said mark reproduced in all image fields for momentarily changing the motor speed to adjust the horizontal lines on the screen JOHN H. HOMRIGHOUS. 

